This review paper, the implications of the recently discovered syndrome of Developmental Amnesia (DA) for two opposing theories of medial temporal lobe (MTL) amnesia are evaluated: Some researchers describe both episodic and semantic memory as subsystems of declarative memory, dependent on medial temporal lobe and midline diencephalic structures, with episodic memory additionally depending on the frontal lobes (Unitary Account). They explain MTL amnesia in terms of an overall impairment in declarative memory functioning. Others describe episodic memory as a memory system that is additional to declarative/semantic memory (Dual-Process Account). They explain MTL amnesia in terms of various patterns of dissociation between episodic and semantic memory functioning. These two opposing accounts are used to interpret studies of the recently discovered syndrome of Developmental Amnesia, a type of childhood-onset amnesia that is characterised by selective damage to the hippocampus and selective episodic memory impairment, and which therefore presents an interesting context for evaluating the two theoretical accounts of MTL amnesia. It is argued that the Hierarchical Account, an elaboration of the Dual-Process Account, presents the most parsimonious explanation of Developmental Amnesia.